A color printing method for implementing a process of pressure development is known. This method includes the steps of exposing a photosensitive medium coated with minute capsules containing color forming materials, activating or deactivating the capsules in accordance with an image, and rupturing the activated capsules by pressurizing the exposed medium. A cycolor medium 1 as illustrated in FIG. 14 is an example of such a medium. The cycolor medium 1 is a medium having a film 2 made of polyester or the like, the film 2 being coated with an infinite number of microcapsules called cyliths 3a to 3c. Each of the cyliths 3a to 3c contains one of color forming materials of cyan, magenta and yellow and a sensitive material called a photo initiator that is sensitive to light of a specific wavelength. The photo initiator contained in each of the cyliths 3a to 3c hardens if it is irradiated with light of a specific wavelength, for example, light of a complementary color of each of the cyliths 3a to 3c. Accordingly, it is possible to deactivate the color forming reaction of a color forming material contained in a cyliths depending on the wavelength of light emitted.
The cycolor medium 1 undergoes pressure development in which the cyliths 3a to 3c of three different colors are irradiated with light and subjected to a high pressure so that the activated cyliths 3a to 3c are crushed. The development method of this kind causes a chemical reaction between the color forming materials contained in the cyliths 3a to 3c and a transparent image-receiving layer called a receiver 4 that is made of polyester or the like, thereby a predetermined color image is recorded (printed) on the cycolor medium 1 which is a recording medium. For example, if only red light is emitted, only the photo initiator contained in the cyliths 3a of cyan hardens. The cyliths 3b of magenta and the cyliths 3c of yellow are crushed due to pressurization, whereby the color forming materials of magenta and yellow develop their respective colors. Thus, those color-forming materials are mixed to develop red color. Similarly, if green light is emitted, the cyliths 3a of cyan and the cyliths 3c of yellow are crushed to develop green color. If blue light is emitted, the cyliths 3a of cyan and the cyliths 3b of magenta are crushed to develop blue color.
Thus, a photosensitive medium such as the cycolor medium 1 needs to be subjected to pressure development after being exposed. As a pressure developing apparatus therefor, pressure means composed of a pair of rollers that are vertically disposed is generally employed. By conveying the cycolor medium (medium) 1 into a gap between the rollers and entirely pressurizing the medium 1, pressure development is performed.
To sufficiently pressurizing the medium using such rollers, those components which are strengthened enough to endure a comparatively high developing pressure, such as rollers, bearings, frames and the like are required. To homogeneously pressurizing the entire medium, at least one of the rollers needs to be shaped like a drum by being subjected to a crowning processing. Thus, the pressure developing apparatus becomes larger, heavier and more expensive.
In view of such backgrounds, it has been considered to replace the conventional pressure developing apparatus employing rollers with a pressure developing apparatus that pressurizes a recording sheet by a small ball (development ball) reciprocating with respect to the surface of a medium (printing sheet or recording sheet) in scanning directions. Since the development ball contacts a point of the surface of the recording sheet, the contact area between the development ball and the recording sheet is very small. Thus, by a small force, it is possible to significantly enhance a pressure per area, so that the pressure developing apparatus can be made smaller and lighter than those employing rollers. Further, since the development ball does not necessitate a special processing such as a crowning processing, the pressure developing apparatus and the recorder employing the pressure developing apparatus can be provided at low costs.
FIG. 15 illustrates an example of the recorder (printer) employing a pressure developing apparatus having a development ball. The recorder 10 has an exposure unit 20 for exposing the aforementioned cycolor medium 1 to form an image, a pressure developing apparatus 30 moving along the surface of the medium 1 exposed by the exposure unit 20 in scanning directions that are perpendicular to a sheet-conveying direction A to perform pressure development, a slab-like face plate (supportive plate or platen) 11 disposed above the pressure developing apparatus 30, and a sheet-conveying mechanism 60 for conveying the medium 1 exposed by the exposure unit 20 toward the pressure developing apparatus 30 by sandwiching the medium 1 between a main roller 61 and an auxiliary roller 62. The exposure unit 20 and the pressure developing apparatus 30 are mounted on a carriage 53, which reciprocates along carriage shafts 51 and 52 extending in the scanning directions by drive means such as a motor 6 and a timing belt 7. The exposure apparatus 20 reciprocates in the scanning directions to expose the medium dot by dot, thus forming an image. Then the pressure developing apparatus 30 sequentially perform pressure development of the exposed medium 1, thus outputting a color-printed cycolor medium. As a matter of course, the arrangement of the platen 11 and the pressure developing apparatus 30 can be reversed. Further, it is also possible to horizontally arrange the platen 11 and the pressure developing apparatus 30.
The exposure apparatus 20, which can employ an LED head 21 having LED's capable of irradiating the medium 1 with three different lights of red (R), green (G) and blue (B), is moved by the carriage 53 to irradiate each of the cyliths 3a to 3c forming each dot with a light of a suitable color. Thus, it is possible to deactivate the cyliths 3a to 3c dot by dot on the basis of image data sent from a personal computer or the like, and to record the image on the cycolor medium 1 (to expose the cycolor medium 1).
The pressure developing apparatus 30 moves together with the exposure apparatus 20 and performs pressure development of the exposed medium 1 that has been conveyed by the sheet-conveying mechanism 60. The pressure developing apparatus 30 has a rectangular parallelepiped housing 31 extending toward the medium 1 and a development ball 39 partially protruding from the side of the medium 1 of the housing 39. The development ball 39 is pressed against the platen 11 by a spring 37 accommodated in the housing 31. It is possible to perform pressure development of the medium 1 by sandwiching the medium 1 between the platen 11 and the development ball 39.
The pressure developing apparatus 30 employing the development ball 39 as described above can pressurize the medium 1 over an extremely small (local) area that is almost considered to be a spot or a point. As the pressure developing apparatus 30 moves, the point to which a pressure is applied continuously moves. Thus, it is possible to ensure a pressure level sufficient to perform development with a relatively small force as obtained from a simple elastic body such as a thin spring or an elastic mechanism. Thus, it is unnecessary to use a large roller, whereby the entire recorder can be significantly reduced in size and weight. Further, since the development ball moves by revolving along the surface of the medium 1, it is possible to pressurize the medium 1 without causing a damage thereto. Therefore, by employing the pressure developing apparatus 30 thus constructed, it becomes possible to reduce the recorder 10 in size and weight, and to provide a recorder that is capable of outputting a high-quality color print at low costs.
However, it has been considered to further improve the aforementioned pressure developing apparatus 30 to make it possible to provide a recorder that is more compact and less expensive. For example, the pressure developing apparatus as illustrated in FIG. 15 is designed such that the carriage shaft 52 receives a reaction force generated in performing pressure development via the carriage 53 and that the pressure developing apparatus 30 moves along the carriage shaft 52. Accordingly, the reaction force for performing pressure development increases a frictional force generated between the carriage 53 and the carriage shaft 52. To reciprocate the carriage 53 smoothly along the carriage shafts 51 and 52, it is necessary to prepare a drive motor having sufficient large outputs to counteract the frictional force. A drive motor with a great driving force is bulky and requires a large installation space. Therefore, an attempt to ensure an installation space for such a high-output drive motor poses a serious problem in reducing the size of the recorder.
The drive motor with high outputs is accompanied by high power consumption. In the recorder employing the cycolor medium 1, the exposure apparatus is a contactless type and can be reduced in size, and expendable supplies such as a ribbon, a toner and the like are not required. Thus, the recorder of this manner can be reduced to a size genuinely suited for conveyance. To realize a portable recorder, it is required that the recorder be capable of operating for a long period of time with a power source of limited energy such as a battery. Hence, it is necessary to reduce the electric power consumed by a drive motor to the minimum possible value. In addition, since a large motor requires a high cost, it is desirable to use a low-power motor with a view to reducing the cost of the recorder.
Therefore, for the purpose of reducing the size and cost of the recorder as well as power consumption, it is indispensable to downsize the drive motor. It is thus an object of the present invention to provide a pressure developing apparatus that can be driven with less power and apply a sufficient pressure. That is, the present invention aims at providing a pressure developing apparatus that can be moved in scanning directions with a small force and develop a high-quality color print by sufficiently pressurizing the medium. It is another object of the present invention to downsize the recorder by making the pressure developing apparatus to be installed in a narrow space. It is still another object of the present invention to reduce the motor power necessary for moving the carriage including the pressure developing apparatus and to realize a compact and low-cost recorder that is low in power consumption and suited for conveyance.